Tuning circuits



Patented Feb. 6, 1940 UNITED sTArEs PATENT A oFFicE.

, TUNING omcurrs 1 Carel Jan van Loon, Eindhoven, Netherlands, as?

signor, by mesne assignments, to Radio Corpo ration of America, New' York, N. Y., a corporation of Delaware Application October 15, 1937,. serial No..169,100

In Germany November 2,1936 j '7 Claims.

The invention relates to a circuit-arrangement for facilitatingthe tuning of a radio-receiving apparatus by means of a device which operates when the receiver is' correctly tuned. Such devices are'particularly important in superheterodyne receiving apparatus with which it is often.

, ative, for example, by means ofa relay when the receiver is correctlyv tuned. Y I

Such a tuning-facilitating device must, of course, be preceded by ;-selec,tive controlling means comprising, for example, tuning circuits, which meansensure that the device can. only operate in a comparatively narrow. band .-of fre'- quencies. It, has previously been proposed to rectify the output vloltage. of these selective means so that a direct current voltage is obtained which was utilized for controlling the tuning facilitating device, the] circuit arrangement being such that the width of the band of frequencies within which said control voltage occurredpwas substantially independent of the signal amplitude. gficcording tothe invention, the control of the said device is efiectedby an auxiliary alternatingvoltage of comparatively .low frequency which is combined. with the high 'or] intermediatefrequency. signals in such manner that it can only have effect in a comparatively narrow band of frequencies in the neighborhood of the correct tuning, an extremely simple andreliable control being thus obtained. H

A further advantage is that for the amplification of the control voltage use may be made of an alternating current amplifier. As appears from the following it is, possible to utilize as such the amplifiers intended for the, amplification of the signal voltages. The auxiliary alternating voltage should preferably be taken -fro 1 n the power mains. p

The invention isillustrated in the accompanying drawing, wherein Fig. l is a block diagram of acircuit embodying one form of the invention, Fig. 2 discloses .a modified form of circuit shown in greater detail, and Figl 3'shows a modification of. a portion of the circuit shown in Fig 2.

Referring now to Figure 1 the block 9 denotes a high-frequency amplifier, 2 a local oscillator and 3 an intermediate-frequency amplifier. The interm'ediatefrequency oscillations amplified are demodulated in a device 4. The low-frequency "oscillations produced are supplied, if desired after.

further. amplification, to a load '5, as for example, a loudspeaker. I v

For the actuation of the tuning facilitating deviceis used 'a side-channeliwhich is connected, at a suitable point to the intermediate-frequency amplifier. The use of such a side-channel for controllin'g'purposes, is known in itself. .With the known circuit arrangements the oscillations are .led through a selective devicewhich only passes avery narrow band of frequencies; the output energy is-rectified and controlsa relay .by which the brake, or ,the'optical indicating device, is

operated,

.Accorc'ling to the invention,'.the intermediate- 20 frequency oscillations are modulated in a device 5 with an auxiliary alternating voltage which maybe, taken,-'for example, through a trans formeri from the power mains.; The oscillations thus modulated are subsequently passed through a selective device 8 which transmits a narrow band of frequencies, whereupon the energy. transmitted is demodulated in 9 and, if de-' sired,' is furtheramplified. Into the output-circuit may be connected an alternating current relay m which is consequently put into operation when correct tuning is obtained. It is ofv course the relay',in which event use may be made of a direct current relay. The relay may be formed as a brake or may actuate a braking device.

'Th'ereisfurther required a device for the puralso possible to utilize for the purpose described the amplifying tubes which are present already. The control voltage may be introduced into the. high-frequency portion I, or the. intermediatefrequency amplifier 3. In this case it is 'neces- ,sary, or at least desirable, to cause this voltage to disappear again after correct tuning has been attained.

possible to rectify the energizing current for A circuit arrangement whereln particular amplifying tubes are not required is shown in Fig.

2 which is more detailed than Fig. 1. The tube l3 in Fig. Zis assumed to serve for the amplification of the intermediatefrequency oscillations set up condenser E 5.

25. connected to a contact of a change-over device ity, is'coupled withthe-circuit M by means, of a The voltage across the two circuits I l and it are rectified by diode rectifiers lfi and 2! respectively. The circuit of the rectifier it comprises resistances il and i8. The resistance iii forms at the same time part of the circuit of the rectifier 25 which comprisesin addition,

a resistance 26 and part of a resistance 39, which is connected in the cathode supply lead of a tube On the resistance H is a slidable tap which is This device comprises a switch 23 which occupies,

when there is no tuning, the position shown, so

that the-upper end of the resistance 20 isconnected through a resistance and a condenser 24 to thegrid of the first low-frequency amplifier.

In the other position of the switch the tap on v the resistance l? is connected to the said grid through the condenser 24. There is provided, furthermore, another low-frequency amplifying tube 26 the anode circuit of which includes an output transformer 2'! whose secondary winding supplies a loudspeaker 28. In the position. shown, that is to; say whenthere is no tuning, the loudspeaker is disconnected, howevenfrom the secondary winding by a switch 29 and the relay 3% is connected to said winding. The relay 35] may be formed as a brake which acts, when correct tuning is attained, on a brake disc 32 with the result that furtherturning of a tuning knob 3| 1 ismade difiicult. In the lead connecting the circuit 6 l to earth are included a switch i l-and a source of voltage 38 which furnishes a voltage of low frequency, e. g., of 50 cycles per second. The

output circuit further comprises a switch 33' by means of which therelay 36 may be changed over to the secondary winding of a. transformer 40. The primary winding of this transformer? is connected to the alternating current supply. The relaytfi is formed as an alternating current relay.

The switches 22, 23, 25),33 and 3! are mutually coupledas indicated by the dot andda'shlines. When the brake responds they are simultaneously actuated.

The circuit arrangement shown acts; as follows:

When there is no tuning, all the switches occupy the positions shown. The circuits [4 and I9 and, also theattendant rectifiers l6 and 2! with the resistances l1, l8 and 2B serve to limit the control of the relay'tll to a narrow band of frequencies. The nearer to tuning one comes on turning the knob 3|, the more the amplitude of the voltage set upv across the circuit M, increases. Even when there is no tuning, direct current voltages are consequently set up acrossfthe resistances i! and .58 by reason of "the normal voltage drop in the cathode resistor 39 of the tube '25. The voltage across the resistance 53 is operative in the circuit of the rectifier 2!, that is to say in such a sense thatanegative bias. is applied to the anode. Only atcorrect tuningjwhen' the voltage across the circuit l9 due to the signal acquires a comparatively high value in excess of the negative bias applied to the anode of the rectifier 2| can consequent rectification take pla'ce- Conseresistance 29. The constant negative bias which -':'5

iquently only when correct tuning is attained is there setup a direct current voltage across the is brought about by the upper part of the resistance'39 has for its purpose to prevent rectification in the rectifier 21' when the variable bias I voltage across the resistance l8 still has-a small value.

Owing to the presence of the sourceof voltage I 38 the intermediate-frequencyoscillations are: i modulated with a' frequency of;50 cycles per sec-, end. However, when thereis no tuning this frequency cannot reach the grid of the tube 25 since in this case a voltage is not yet set up across thefl o resistance An alternating voltage component of 50 cycles per second does not occur across the i v resistance 20 until the circuit I9 rectifies; that is to'sayuntil correct tuning. is 'obtained. This y component is amplified by the low-frequency am- 15 I plifying tubes and 2B, andcauses the relay 3!] included in the output circuit -to respond with the result that any further rotation of the knob 3| is prevented.

At the, same time the relay actuates the '0 I f switches 22,23, 29,33 and 31 so that,a;fter tuning has been efiectejd, they are placed in the-other Y switch position. Simple consideration shows that the apparatus is now suited to normal broadcast reception. The diode, Hifacts now as a. de'- 35 tector, the low-frequency signal .voltages are I I taken from the' resistance H, "and supplied through the condenser Ell-to the grid of the first low-frequency tube 25. Since the switchjZZjis closed, the rectified voltagelof the circuit 19 can no longer act on that of the circuit It. The source of voltage 38 is switched outof 'cir-.

cuit sothat the; auxiliary voltage is caused to dis- 1 a appear, but the relay remains in the operating position owing to the switch 33 being shifted to the lower contact in which casethe relay 30 is maintained energized through the transformer d0 connected to the A. C. supply. j

If it isdesired to tune toanother station, the v relay has to be set again. out of operation. Tott? thatendthe tuning knob may be'associated with a switch device which is actuated, for example by a longitudinal motion of the knob or by rotation Y of the'latter through a determined angle, for example, against the actionof a spring.

It is not necessary that the introduction of the additional alternating voltage shouldfbe effected bymodulatingthe intermediate or highfrequencysignals with this voltage and by dcmodulating them afterwards again. Another s f possibility consists in that the source ofadditional voltage is operative in the circuit of the. rectifier 2|. voltage component having .a frequency, of-w5 0 cycles per second cannot be. set up across the resistance before the diode 2i 'rectifies, that is to say before correct tuning is obtained. This .possibility is shown in Fig. According to. this: mode of realization the source of voltage '38 is located between the anode of the rectifier 2| and the circuit M. It may be adapted to be switched 1 out ofcircuit, but this is not-necessary under all Y conditions. What I claim is:'

1. A system for determining accurate tuning I of a radio receiver comp-rising a braking device -operatively related to the tuning. mechanism of the receiver and preventing further adjustment of the tuning mechanism when in accurately tuned position, a relay for actuating the braking device, a locally produced auxiliary source of low frequency voltage superimposed on the receiver circuit for energizing the relay, and means included in said circuit for blocking transmission of said auxiliary voltage to the relayexcept ref Also in this .case an alternating;

when the receiver is in accurately tuned condi the receiver circuit for energizing the relay, and

circuit means permitting transmission of said auxiliary voltage to the relay only when the receiver is in accurately tuned condition.

3. A system as defined inclaim 2 wherein the brake actuating relay operates to disconnect the auxiliary, source of voltage upon accurate tuning adjustment of the receiver.

4. The combination with a radio receiver hav-" ing a high frequency portion, a signal detector and'a low frequency portion, of means for facili-v tating accurate tuning of the receiver, said means comprising a braking device operatively related adapted to prevent further adjustment of the I tuning mechanism when in accurately tuned position, a relay associated with the low frequency portion, of the receiver for actuating the braking device, a" locally produced auxiliary source of low frequency voltage superimposed on the high frequency portion of the receiver for energizing the relay, and means associated with the signal detector for blocking transmission of said auxiliary voltage to the relay except when the receiver isin accurately tuned condition.

5. The combination with a radio receiver having a high frequency portion, a signal detector, v

the signal detector for preventing the transmisa low-frequency portion and a sound reproducer, of means for facilitating accurate tuning of the receiver and preventing further adjustment of the receiver tuning mechanism when in accurate tuning position, comprising a braking device operatively related to the tuning mechanism a relay associated withthe low frequency portion of the to the tuning mechanism of the receiver and imposed on the high frequency portion of the receiver for energizing the relay, circuit, means operating in conjunction with the signal detector permitting transmission of said auxiliary voltage to the relay only when the tuned circuits of the receiver are so adjusted to pass a comparatively narrow band offrequencies in the neighborhood of correct tuning, and means controlled by the relay in its operative condition to discon-- nect theau'xiliary source of voltage and to connect the signal detector directly to the low fre- .quency portion of the receiver. I 6. In a receiving circuit, a signal channel comprising a high. frequency amplifier portion, a detector and a low frequency amplifier portion, means for adjusting the tuning of the receiver, a brake member associated with said tuning means and operative only when the receiving circuit is in accurately tuned condition, and means for controlling the operation of said brake member comprising a'locally produced source of low frequency voltage, and circuit means associated with the detector for preventing the transmission of the low frequency voltage when the receiving circuit issusbtantially off" tune.

7. In a receiving circuit, a signal channel, com

prising a high frequency amplifier :portion, a signal detector and a low frequency amplifier portion, means for adjusting the tuning of the re ceiver, a brake member associated with said tun ing means and operative'only when the receiving circuit is adjusted to pass a comparatively nar+ row band of frequencies in the neighborhood of correct tuning, means for controlling the operation of said brake member comprising a source of low frequency voltagewhichis impressed'on the signal channel, circuit means associated with sion of the low-frequency voltage except only when the receiving circuit is in substantially correct tuning adjustment, and means controlled by the relay after the correct tuning adjustment hasbeen made for disconnecting the auxiliary source of voltage and also the circuit means associated with the signal detector.

CAREL JAN VAN LOON. 

